In a conventional pneumatic tire of the “tubeless” type (that is to say of the type without an inner tube), the radially internal face comprises an airtight layer (or more generally a layer that is impermeable to any inflation gas) which enables the pneumatic tire to be inflated and kept under pressure. Its airtightness properties enable it to guarantee a relatively low rate of pressure loss, making it possible to keep the tire inflated, in the normal operating state, for a sufficient time, normally several weeks or several months. It also has the role of protecting the carcass reinforcement from the diffusion of air coming from the internal space of the tire.
This role of airtight inner layer or “inner liner” is today fulfilled by compositions based on butyl rubber (isobutylene/isoprene copolymer), long renowned for their excellent airtightness properties.
However, one well-known drawback of compositions based on butyl rubber or elastomer is that they have high hysteresis losses, furthermore over a wide temperature range, which drawback degrades the rolling resistance of pneumatic tires.
Reducing the hysteresis of these airtightness inner layers and therefore, in fine, the fuel consumption of motor vehicles, is a general objective which current technology comes up against.
However, the inventors discovered, during their research, that an elastomer other than butyl makes it possible to obtain airtight inner layers that respond to such an objective, while providing the latter with very good airtightness properties.
Thus, according to a first object, the present invention relates to an inflatable article equipped with an elastomer layer impermeable to inflation gases such as air, said elastomer layer comprising at least, as the predominant elastomer, a thermoplastic stirene/isobutylene/stirene (SIBS) elastomer.
Compared with butyl rubbers, SIBS has also the major advantage, due to its thermoplastic nature, of being able to be worked as is in the molten (liquid) state, and consequently of offering a possibility of simplified processing.
The invention particularly relates to inflatable articles made of rubber such as pneumatic tires, or inner tubes, especially inner tubes for a pneumatic tire.
The invention relates more particularly to the pneumatic tires intended to be fitted on motor vehicles of the passenger type, SUV (Sport Utility Vehicle) type, two-wheeled vehicles (especially motorcycles), aircraft, industrial vehicles chosen from vans, heavy vehicles—that is to say underground trains, buses, road transport vehicles (lorries, towing vehicles, trailers), off-road vehicles, such as agricultural and civil-engineering vehicles—and other transport or handling vehicles.
The invention also relates to a process for sealing an inflatable article with respect to inflation gases, in which a gastight elastomer layer as defined above is incorporated into said inflatable article during its manufacture or is added to said inflatable article after its manufacture.
The invention also relates to the use, in an inflatable article, of an elastomer layer as defined above as a layer impermeable to inflation gases.